arm64:ilp32: add vdso-ilp32 and use for signal return

maillist inclusion
category: feature
bugzilla: 46790
CVE: NA

Reference: https://github.com/norov/linux/commits/ilp32-5.2



--------------------------------

ILP32 VDSO exports following symbols:
 __kernel_rt_sigreturn;
 __kernel_gettimeofday;
 __kernel_clock_gettime;
 __kernel_clock_getres.

What shared object to use, kernel selects depending on result of
is_ilp32_compat_task() in arch/arm64/kernel/vdso.c, so it substitutes
correct pages and spec.

Adjusted to move the data page before code pages in sync with
commit 601255ae ("arm64: vdso: move data page before code pages")

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Signed-off-by: Bamvor Jian Zhang <bamv2005@gmail.com>
Signed-off-by: Yury Norov <ynorov@marvell.com>

 Conflicts:
	arch/arm64/Makefile
	arch/arm64/kernel/Makefile
	arch/arm64/kernel/asm-offsets.c
	arch/arm64/kernel/vdso.c
	arch/arm64/kernel/vdso/gettimeofday.S
[wangxiongfeng: rewrite vdso-ilp32/Makefile according to vdso/Makefile]
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>